(a) Field of the Invention
The present invention relates to a backlight unit for a liquid crystal display.
(b) Description of Related Art
Display screens, such as computer and television monitors, are usually made of either self-emitting displays or non-emitting displays. Examples of self-emitting displays include light emitting diodes (LEDs), electroluminescences (ELs), vacuum fluorescent displays (VFDs), field emission displays (FEDs) and plasma display panels (PDPs). A commonly used non-emitting display includes liquid crystal displays (LCDs). Non-emitting displays, unlike self-emitting displays, require a light source.
An LCD includes two panels coupled with field-generating electrodes and a liquid crystal (LC) layer with dielectric anisotropy interposed therebetween. When electric voltages are applied to the field-generating electrodes, an electric field is generated in the liquid crystal layer in response to the voltages. Light transmittance through the LC layer varies depending on the electric field. Thus, light transmittance is controlled by varying the applied voltages. By manipulating the applied voltages, desired images are displayed on the liquid crystal display.
The LCD being a non-emitting type of display, the light that is used to display the images is supplied by a separate source. This separate source may be an artificial light source such as a lamp coupled to the LCD, or a natural source like the sun. When using an artificial light source, the total brightness of the LCD screen is usually adjusted by either using an inverter to regulate the ratio of the on and off signals supplied to the light source or by regulating the current through the light source.
Typically, a large LCD requires several light sources (e.g., lamps) for uniform luminance across the LCD. When several lamps are used, the lamps are driven by a driving circuit, such as an inverter, for cost efficiency. When multiple lamps are used, however, there is a downside of not being able to easily detect a malfunctioning of one of the lamps, which may be caused by the one lamp being improperly mounted or simply defective. Malfunctioning of one lamp is highly undesirable as it may cause arcs near electrodes of the lamp. Aside from being a visual imperfection on the display, the arcs can pose a hazard by causing fire. A method of detecting a malfunctioning lamp is desired.